Cancer Gone Viral: Viruses that treat cancer?
Cancer therapy Oncolytic viruses virus

Cancer Gone Viral: Viruses that treat cancer?

Dr. Talia Henkle
Dr. Talia Henkle

In 10 seconds? Multiple types of viruses can help treat cancer due to their cancer-targeting and immune-boosting properties. The FDA approved a version of this method in 2015 to treat some types of skin cancer, and many other cancer-killing viruses are currently being investigated!

Wait, what? Viruses can treat cancer? I get it. It’s confusing! In our Cancer Gone Viral series, we've been focusing on ways that viruses cause cancer. But it turns out that there are different types of viruses that can be used to treat cancers as well–called oncolytic viruses (onco = cancer, lytic = cell rupturing). Many different types of viruses and treatment strategies are under investigation and the first oncolytic virus cancer therapy was FDA-approved to treat advanced melanoma (a type of skin cancer) in 2015.

How can a virus treat cancer? Viruses can tackle cancer through their ability to directly infect and kill cancer cells as well as their capacity to get the immune system’s attention. But of course, this is only helpful if the virus primarily infects the tumor and doesn’t make the patients sick!

Yeah… so, how can researchers be so sure these viruses won’t attack our healthy cells? Multiple ways–from taking advantage of natural viral properties to engineering viruses to have unique properties. For example, some features of cancer cells make them easier for viruses to infect. To get inside (AKA infect) our cells, viruses must first latch onto something on our cells' surfaces (AKA the entry receptor – remember ACE2 from Covid times?). And some tumor cells have much higher levels of certain viruses’ entry receptors on their surfaces than healthy cells. That means that several types of viruses preferentially infect, and subsequently kill tumor cells over our bodies’ healthy cells.

Well, that seems like good luck… I know targeting tumors with treatments can be complicated! But there’s a scientific reason for this madness! In our Cancer Gone Viral series so far, we’ve talked about how several cancer-causing viruses use tactics to encourage cells to divide so that the viruses can complete their life cycle. But because cancerous cells are already dividing rapidly, once oncolytic viruses infect those cells, they can quickly make more viruses, kill the cells, and release the new viruses to infect nearby cells (hopefully tumor cells!). Another factor facilitating oncolytic virus infection is that many tumors acquire mutations that disrupt their anti-viral capabilities (AKA Type I interferon mechanisms).  That means that oncolytic viruses cause damage to tumor tissues much more quickly than they might in healthy cells since higher Type I Interferon activity typically slows the virus down.

Proposed method by which the HSV-1 engineered oncolytic virus may work to treat cancer. Source: Ferrucci PF, et al. Cancers: 2021;13(1383)

Got it. And you mentioned the immune system? Yes! By the time cancer forms, our immune systems are dazed and confused by the cancer's immune escape tactics. Oncolytic virus infection of tumor cells will help refocus our immune system on the task at hand. As the tumor cells rupture and die from the infection they release mutated tumor proteins as well. Our immune system will often view these mutated proteins similarly to viral proteins–as 'foreign invaders'–and form an army to take them out along with the virus. So, even if oncolytic viruses don’t infect every tumor in someone’s body, they can help jumpstart an anti-tumor immune response that can help attack tumors far from the site of infection!

OK. Can I get an example of how this has helped patients? Coming right up! Funnily enough, the oncolytic virus that has been FDA approved to treat skin cancer patients is an artificially engineered version of a Herpesvirus–the family of viruses that is most notorious for causing cancer! Scientists have created a version of the Herpes Simplex Virus-1 (AKA HSV-1, the virus known for causing cold sores) that removes many of its harmful properties and adds in the capacity for the virus to produce an immune-boosting protein (called GM-CSF for my immunology nerds out there). In a clinical trial of patients with advanced skin cancer, after treatment with this engineered oncolytic virus, about 10% of patients’ tumors went away–even among some patients who had metastatic disease (the most difficult to treat!). While these results certainly have room for improvement, they showcase viruses' life-saving potential and motivate researchers to keep exploring new possibilities!

Other viruses that can tackle cancer

Some viruses don't need to be modified at all to have cancer-killing properties. Scientists have seen varying levels of success in treating cancers using naturally-occurring viruses that don't usually cause any symptoms in humans (like the coxsackievirus) or those that typically infect other animals (like the avian Newcastle disease virus, or vesicular stomatitis virus that typically infects insects, horses, cows, and pigs).

With so many different types of cancers, specific types of viruses will likely be helpful in treating specific types of cancers. And these naturally-occurring cancer treatments (AKA oncolytic viruses) may be chilling right under our (or our pets') noses as we speak!

Dr. Talia Henkle has distilled 2 research papers, saving your 7 hours of reading time

The Science Integrity Check of this 3-min Science Digest was performed by Dr. Jacquelyn Bedsaul.

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